1. Field of the Invention
The present invention relates to a terminal structure connected through a conductive adhesive to an electrode of a piezoelectric element and having a terminal face on a metal layer connected to a wiring layer, a flexure employing the terminal structure, and a head suspension employing the flexure.
2. Description of Related Art
Information devices are rapidly getting smaller and elaborated, and for use with such information devices, needs for micro-actuators capable of conducting positioning control for very small distances are increasing. The micro-actuators are highly needed by, for example, optical systems for correcting focuses and inclination angles, ink jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives increase their storage capacity by increasing the number of tracks per inch (TPI) of a magnetic disk, i.e., by narrowing the width of each track on the magnetic disk.
The magnetic disk drives, therefore, need an actuator capable of precisely positioning a magnetic head across tracks within a minute range.
To meet the need, Japanese Unexamined Patent Application Publication No. 2010-086649 discloses a head suspension with a dual actuator system. The dual actuator system employs a piezoelectric element in addition to a usual voice coil motor that drives a carriage to which the head suspension is attached. The piezoelectric element is arranged between a base plate and a load beam of the head suspension, to minutely move a magnetic head attached to a front end of the load beam.
According to the head suspension of the dual actuator system, the voice coil motor turns the head suspension through the carriage, and in addition, the piezoelectric element deforms in proportion to a voltage applied thereto, to minutely move the magnetic head at the front end of the load beam in a sway direction (a widthwise direction of the load beam) relative to the base plate. With this, the head suspension is able to precisely position the magnetic head to a target position on a magnetic disk.
The dual actuator system supplies electricity to the piezoelectric element through a flexure attached to the load beam. The flexure includes a terminal structure to electrically connect through a conductive adhesive as a conductive bonding part the flexure and piezoelectric element to each other.
FIGS. 19A, 19B, and 19C are views illustrating a terminal structure for a terminal of a flexure according to a related art.
In FIGS. 19A to 19C, the terminal 201 includes a metal layer 203, an insulating layer 205 formed on the metal layer 203, and a wiring layer 207 formed on the insulating layer 205. The metal layer 203 faces an electrode 211 of a piezoelectric element 209. Through the metal layer 203 and insulating layer 205, a through hole 213 is formed to expose a terminal face 215 of the wiring layer 207 toward the electrode 211 of the piezoelectric element 209.
The terminal face 215 is adhered to a conductive adhesive 217 that is filled in the through hole 213 between the terminal 201 and the piezoelectric element 209, thereby electrically connecting the wiring layer 207 of the terminal 210 to the electrode 211 of the piezoelectric element 209.
According to the related art, the terminal structure of the terminal 201 limits the terminal face 215 within an area of the wiring layer 207 exposed in the through hole 213. Namely, an adhering area of the terminal face 215 of the wiring layer 207 is limited by the through hole 213.
As a result, the terminal structure according to the related art is unstable in electrical connection between the terminal face 215 and the conductive adhesive 217 and is insufficient in bonding strength between the same.
In connection with the electrical connection between the terminal face 215 and the conductive adhesive 217, stress such as heat applied to the terminal face 215 and conductive adhesive 217 may temporarily break the electrical connection, and when the stress is removed, the electrical connection may resume. In this way, the electrical connection at the terminal structure according to the related art is unstable.
According to the related art, no improvement is expected in the unstableness of the electrical connection even if the terminal face 215 is gold-plated to improve electrical conductivity with respect to the conductive adhesive 217.
In connection with the bonding strength between the terminal face 215 and the conductive adhesive 217, peeling tests show that an interface between the terminal face 215 and the conductive adhesive 217 frequently breaks as adhesive failure even when the conductive adhesive 217 causes no breakage as cohesive failure. This means that, according to the related art, the bonding strength between the terminal face 215 and the conductive adhesive 217 is inferior.
In this way, the terminal structure according to the related art is unstable in electrical connection and weak in bonding strength between the terminal face 215 and the conductive adhesive 217.